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Tropical Storm Isaac Forecast Discussion Number 22
2018-09-13 04:53:46| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Wed Sep 12 2018 907 WTNT44 KNHC 130253 TCDAT4 Tropical Storm Isaac Discussion Number 22 NWS National Hurricane Center Miami FL AL092018 1100 PM AST Wed Sep 12 2018 A NOAA P-3 Hurricane Hunter plane has been investigating Isaac this evening, and the data show that the cyclone has weakened a bit. The maximum 850-mb flight-level wind measured by the plane was 47 kt, and the highest SFMR winds not coincident with a rain spike were around 45 kt. Based on these wind data, the initial intensity is lowered to 45 kt, and the minimum pressure is up to 1006 mb based on dropsonde data. Additionally, a superposition of the flight-level wind and dropsonde surface wind data suggest that Isaac may not have a closed circulation at 850 mb but is still hanging on to one at the surface. All of Isaac's deep convection is displaced 60-120 n mi to the northeast and southeast of the low-level center due to around 30 kt of westerly shear. This magnitude of the shear is not expected to decrease during the next 12-24 hours, so at the very least, gradual weakening is anticipated. With the circulation so fragile and limited to below 850 mb, however, it's entirely possible that Isaac could open up into a wave at any time. Even if degeneration into a wave occurs, the system would likely carry tropical-storm-force winds across the Leeward Islands on Thursday. After Isaac moves into the eastern Caribbean Sea, there is a lot of uncertainty regarding its future. The 18Z GFS has come back in line with the ECMWF, showing Isaac opening up into a trough over the central and western Caribbean Sea, but the environmental conditions (lower shear, warm sea surface temperatures, etc.) would suggest that the system would have an opportunity to restrengthen. For now, the new NHC intensity forecast maintains continuity from the previous advisory, showing gradual weakening through 48 hours and then holding the system at 35 kt through day 5. This remains a low confidence forecast until we know if Isaac survives the next couple of days. Isaac continues to move quickly westward with an initial motion of 270/17 kt. The track guidance remains tightly clustered on a nearly due westward motion for much of the forecast period, with some of the same speed differences noted in previous forecasts. Especially since Isaac's speed has been faster than forecast, the NHC track forecast continues to favor the faster guidance, in particular the ECMWF, GFS, and HCCA models. Reconnaissance and scatterometer data suggest that there are no tropical-storm-force winds within the southern semicircle, but the radii we've been carrying within the northern semicircle appear reasonable. The wind radii forecast have been adjusted to account for the new initial radii. Key Messages: 1. Isaac is expected to still be producing tropical-storm-force winds when it moves across the Lesser Antilles on Thursday, and tropical storm warnings are in effect for Martinique, Dominica, and Guadeloupe. Tropical storm watches are in effect for Montserrat, St. Kitts and Nevis, Antigua, Saba and St. Eustatius, St. Maarten, and St. Martin. Interests on those islands should follow any advice given by their local officials. 2. Life-threatening flash flooding is possible with Isaac. The storm is expected to produce total rainfall accumulations of 2 to 4 inches with isolated amounts up 8 inches across Martinique, Dominica and Guadeloupe. Rainfall amounts of 1 to 2 inches with isolated amounts to 4 inches are expected across Puerto Rico and the southern United States Virgin Islands. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 15.3N 58.0W 45 KT 50 MPH 12H 13/1200Z 15.5N 60.4W 45 KT 50 MPH 24H 14/0000Z 15.6N 63.4W 40 KT 45 MPH 36H 14/1200Z 15.7N 66.4W 40 KT 45 MPH 48H 15/0000Z 15.7N 69.2W 35 KT 40 MPH 72H 16/0000Z 15.6N 73.9W 35 KT 40 MPH 96H 17/0000Z 16.5N 77.5W 35 KT 40 MPH 120H 18/0000Z 17.5N 82.0W 35 KT 40 MPH $$ Forecaster Berg
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Tropical Storm Isaac Wind Speed Probabilities Number 22
2018-09-13 04:53:13| National Hurricane Center (Atlantic)
Issued at 0300 UTC THU SEP 13 2018 217 FONT14 KNHC 130253 PWSAT4 TROPICAL STORM ISAAC WIND SPEED PROBABILITIES NUMBER 22 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092018 0300 UTC THU SEP 13 2018 AT 0300Z THE CENTER OF TROPICAL STORM ISAAC WAS LOCATED NEAR LATITUDE 15.3 NORTH...LONGITUDE 58.0 WEST WITH MAXIMUM SUSTAINED WINDS NEAR 45 KTS...50 MPH...85 KM/H. Z INDICATES COORDINATED UNIVERSAL TIME (GREENWICH) ATLANTIC STANDARD TIME (AST)...SUBTRACT 4 HOURS FROM Z TIME EASTERN DAYLIGHT TIME (EDT)...SUBTRACT 4 HOURS FROM Z TIME CENTRAL DAYLIGHT TIME (CDT)...SUBTRACT 5 HOURS FROM Z TIME WIND SPEED PROBABILITY TABLE FOR SPECIFIC LOCATIONS CHANCES OF SUSTAINED (1-MINUTE AVERAGE) WIND SPEEDS OF AT LEAST ...34 KT (39 MPH... 63 KM/H)... ...50 KT (58 MPH... 93 KM/H)... ...64 KT (74 MPH...119 KM/H)... FOR LOCATIONS AND TIME PERIODS DURING THE NEXT 5 DAYS PROBABILITIES FOR LOCATIONS ARE GIVEN AS OP(CP) WHERE OP IS THE PROBABILITY OF THE EVENT BEGINNING DURING AN INDIVIDUAL TIME PERIOD (ONSET PROBABILITY) (CP) IS THE PROBABILITY OF THE EVENT OCCURRING BETWEEN 00Z THU AND THE FORECAST HOUR (CUMULATIVE PROBABILITY) PROBABILITIES ARE GIVEN IN PERCENT X INDICATES PROBABILITIES LESS THAN 1 PERCENT PROBABILITIES FOR 34 KT AND 50 KT ARE SHOWN AT A GIVEN LOCATION WHEN THE 5-DAY CUMULATIVE PROBABILITY IS AT LEAST 3 PERCENT. PROBABILITIES FOR 34...50...64 KT SHOWN WHEN THE 5-DAY 64-KT CUMULATIVE PROBABILITY IS AT LEAST 1 PERCENT. - - - - WIND SPEED PROBABILITIES FOR SELECTED LOCATIONS - - - - FROM FROM FROM FROM FROM FROM FROM TIME 00Z THU 12Z THU 00Z FRI 12Z FRI 00Z SAT 00Z SUN 00Z MON PERIODS TO TO TO TO TO TO TO 12Z THU 00Z FRI 12Z FRI 00Z SAT 00Z SUN 00Z MON 00Z TUE FORECAST HOUR (12) (24) (36) (48) (72) (96) (120) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - LOCATION KT GUANAJA 34 X X( X) X( X) X( X) X( X) X( X) 3( 3) GRAND CAYMAN 34 X X( X) X( X) X( X) X( X) 1( 1) 6( 7) MONTEGO BAY 34 X X( X) X( X) X( X) X( X) 5( 5) 3( 8) KINGSTON 34 X X( X) X( X) X( X) X( X) 3( 3) 1( 4) PORT-AU-PRINCE 34 X X( X) X( X) 1( 1) 4( 5) X( 5) X( 5) CAPE BEATA 34 X X( X) X( X) 3( 3) 7(10) X(10) 1(11) PUERTO PLATA 34 X X( X) X( X) 1( 1) 1( 2) 1( 3) X( 3) PONCE PR 34 X X( X) 3( 3) 1( 4) X( 4) X( 4) X( 4) AGUADILLA PR 34 X X( X) 1( 1) 2( 3) X( 3) X( 3) X( 3) VIEQUES PR 34 X 3( 3) 4( 7) 1( 8) X( 8) X( 8) X( 8) SAINT THOMAS 34 X 3( 3) 3( 6) 1( 7) X( 7) X( 7) X( 7) SAINT CROIX 34 X 5( 5) 7(12) 1(13) X(13) X(13) X(13) SAINT MAARTEN 34 1 5( 6) 2( 8) X( 8) X( 8) X( 8) X( 8) ST KITTS-NEVIS 34 4 16(20) 1(21) X(21) X(21) X(21) X(21) BARBUDA 34 7 9(16) 1(17) X(17) X(17) X(17) X(17) ANTIGUA 34 11 19(30) X(30) X(30) X(30) X(30) X(30) GUADELOUPE 34 31 40(71) X(71) X(71) X(71) X(71) X(71) GUADELOUPE 50 1 5( 6) X( 6) X( 6) X( 6) X( 6) X( 6) AVES 34 1 37(38) 10(48) X(48) X(48) X(48) X(48) AVES 50 X 4( 4) 3( 7) X( 7) X( 7) X( 7) X( 7) DOMINICA 34 12 23(35) X(35) X(35) X(35) X(35) X(35) DOMINICA 50 1 5( 6) X( 6) X( 6) X( 6) X( 6) X( 6) MARTINIQUE 34 3 3( 6) X( 6) X( 6) X( 6) X( 6) X( 6) $$ FORECASTER BERG
Summary for Tropical Storm Isaac (AT4/AL092018)
2018-09-13 04:52:47| National Hurricane Center (Atlantic)
...NOAA HURRICANE HUNTER AIRCRAFT FINDS ISAAC A LITTLE WEAKER... ...HEAVY RAINS AND TROPICAL-STORM-FORCE WINDS EXPECTED OVER PORTIONS OF THE LEEWARD ISLANDS ON THURSDAY... As of 11:00 PM AST Wed Sep 12 the center of Isaac was located near 15.3, -58.0 with movement W at 20 mph. The minimum central pressure was 1006 mb with maximum sustained winds of about 50 mph.
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Tropical Storm Isaac Public Advisory Number 22
2018-09-13 04:52:47| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Wed Sep 12 2018 336 WTNT34 KNHC 130252 TCPAT4 BULLETIN Tropical Storm Isaac Advisory Number 22 NWS National Hurricane Center Miami FL AL092018 1100 PM AST Wed Sep 12 2018 ...NOAA HURRICANE HUNTER AIRCRAFT FINDS ISAAC A LITTLE WEAKER... ...HEAVY RAINS AND TROPICAL-STORM-FORCE WINDS EXPECTED OVER PORTIONS OF THE LEEWARD ISLANDS ON THURSDAY... SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION ----------------------------------------------- LOCATION...15.3N 58.0W ABOUT 220 MI...355 KM E OF DOMINICA ABOUT 235 MI...380 KM ESE OF GUADELOUPE MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H PRESENT MOVEMENT...W OR 270 DEGREES AT 20 MPH...31 KM/H MINIMUM CENTRAL PRESSURE...1006 MB...29.71 INCHES WATCHES AND WARNINGS -------------------- CHANGES WITH THIS ADVISORY: None. SUMMARY OF WATCHES AND WARNINGS IN EFFECT: A Tropical Storm Warning is in effect for... * Martinique * Dominica * Guadeloupe A Tropical Storm Watch is in effect for... * Antigua * Montserrat * St. Kitts and Nevis * Saba and St. Eustatius * St. Martin and St. Maarten A Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area, in this case within 24 hours. A Tropical Storm Watch means that tropical storm conditions are possible within the watch area, in this case within 24 hours. Interests elsewhere in the Leeward Islands should monitor the progress of Isaac. For storm information specific to your area, please monitor products issued by your national meteorological service. DISCUSSION AND OUTLOOK ---------------------- At 1100 PM AST (0300 UTC), the center of Tropical Storm Isaac was located near latitude 15.3 North, longitude 58.0 West. Isaac is moving toward the west near 20 mph (31 km/h), and this general motion with a decrease in forward is expected to continue through the weekend. On the forecast track, Isaac is forecast to move across the central Lesser Antilles and into the eastern Caribbean Sea on Thursday, and then move across the eastern and central Caribbean Sea through the weekend. Data from a NOAA Hurricane Hunter aircraft and satellite-derived wind data indicate that the maximum sustained winds have decreased to near 50 mph (85 km/h) with higher gusts. A gradual decrease in the winds is forecast during the next 48 hours. Tropical-storm-force winds extend outward up to 175 miles (280 km) to the north of the center. Data from the aircraft indicate that the minimum central pressure is 1006 mb (29.71 inches). HAZARDS AFFECTING LAND ---------------------- RAINFALL: Isaac is expected to produce total rainfall accumulations of 2 to 4 inches with isolated amounts up to 8 inches across Martinique, Dominica, and Guadeloupe. Rainfall of 1 to 2 inches with isolated amounts to 4 inches are forecast across Puerto Rico and the southern United States Virgin Islands, with up to an inch anticipated across the remaining Windward and Leeward Islands. This rainfall may cause life-threatening flash flooding. WIND: Tropical storm conditions are expected within the tropical storm warning area on Thursday. Tropical storm conditions are possible within the tropical storm watch area on Thursday. STORM SURGE: Some coastal flooding is possible in areas of onshore winds. Near the coast, the surge will be accompanied by large waves. SURF: Swells generated by Isaac are affecting portions of the Lesser Antilles. These swells are likely to cause life-threatening surf and rip current conditions. Please consult products from your local weather office. NEXT ADVISORY ------------- Next intermediate advisory at 200 AM AST. Next complete advisory at 500 AM AST. $$ Forecaster Berg
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Tropical Storm Isaac Forecast Advisory Number 22
2018-09-13 04:52:15| National Hurricane Center (Atlantic)
Issued at 0300 UTC THU SEP 13 2018 425 WTNT24 KNHC 130252 TCMAT4 TROPICAL STORM ISAAC FORECAST/ADVISORY NUMBER 22 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092018 0300 UTC THU SEP 13 2018 CHANGES IN WATCHES AND WARNINGS WITH THIS ADVISORY... NONE. SUMMARY OF WATCHES AND WARNINGS IN EFFECT... A TROPICAL STORM WARNING IS IN EFFECT FOR... * MARTINIQUE * DOMINICA * GUADELOUPE A TROPICAL STORM WATCH IS IN EFFECT FOR... * ANTIGUA * MONTSERRAT * ST. KITTS AND NEVIS * SABA AND ST. EUSTATIUS * ST. MARTIN AND ST. MAARTEN A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE EXPECTED SOMEWHERE WITHIN THE WARNING AREA... IN THIS CASE WITHIN 24 HOURS. A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE POSSIBLE WITHIN THE WATCH AREA... IN THIS CASE WITHIN 24 HOURS. INTERESTS ELSEWHERE IN THE LEEWARD ISLANDS SHOULD MONITOR THE PROGRESS OF ISAAC. TROPICAL STORM CENTER LOCATED NEAR 15.3N 58.0W AT 13/0300Z POSITION ACCURATE WITHIN 15 NM PRESENT MOVEMENT TOWARD THE WEST OR 270 DEGREES AT 17 KT ESTIMATED MINIMUM CENTRAL PRESSURE 1006 MB MAX SUSTAINED WINDS 45 KT WITH GUSTS TO 55 KT. 34 KT.......150NE 0SE 0SW 120NW. 12 FT SEAS..150NE 30SE 30SW 150NW. WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT. REPEAT...CENTER LOCATED NEAR 15.3N 58.0W AT 13/0300Z AT 13/0000Z CENTER WAS LOCATED NEAR 15.3N 57.2W FORECAST VALID 13/1200Z 15.5N 60.4W MAX WIND 45 KT...GUSTS 55 KT. 34 KT...120NE 0SE 0SW 90NW. FORECAST VALID 14/0000Z 15.6N 63.4W MAX WIND 40 KT...GUSTS 50 KT. 34 KT... 80NE 0SE 0SW 60NW. FORECAST VALID 14/1200Z 15.7N 66.4W MAX WIND 40 KT...GUSTS 50 KT. 34 KT... 70NE 0SE 0SW 50NW. FORECAST VALID 15/0000Z 15.7N 69.2W MAX WIND 35 KT...GUSTS 45 KT. 34 KT... 70NE 0SE 0SW 50NW. FORECAST VALID 16/0000Z 15.6N 73.9W MAX WIND 35 KT...GUSTS 45 KT. 34 KT... 70NE 0SE 0SW 50NW. EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 150 NM ON DAY 4 AND 175 NM ON DAY 5...AND FOR INTENSITY NEAR 15 KT EACH DAY OUTLOOK VALID 17/0000Z 16.5N 77.5W MAX WIND 35 KT...GUSTS 45 KT. OUTLOOK VALID 18/0000Z 17.5N 82.0W MAX WIND 35 KT...GUSTS 45 KT. REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 15.3N 58.0W NEXT ADVISORY AT 13/0900Z $$ FORECASTER BERG
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